Anthony Martial has been involved in a bust-up with a youth-team player that threatened to give Erik ten Hag another headache after the Cristiano Ronaldo saga.
The Manchester United boss was forced to temporarily halt a training session for non-World Cup players at Carrington on Wednesday. It's understood Martial - one of several senior players not involved in Qatar - was taking part in one of the final sessions before being given a break.
A number of youth-team stars were also drafted in by ten Hag to boost the numbers but events quickly spiralled out of control. It's believed Under-18 star Dan Gore, signed from Burnley last summer, clattered Martial with a robust tackle, which sparked an angry confrontation between the pair.
Martial is alleged to have lashed out and caught the teenager, who is said to have stood his ground against the 26-year-old striker who was snubbed for the World Cup by France boss Didier Deschamps.
The pair were pulled apart, with Gore told by ten Hag and his staff that tackling first-team stars was off-limits in training games.
Martial is believed to have apologised to the youngster - and Gore was happy to make the peace.
United insiders insist that it was the kind of flash point that is common at a top-flight club, where the pressure to impress is intense.
Gore, described as a tenacious tackler by United's website, rejoined the session. He is rated highly by Ten Hag and United's academy staff. The United boss has encouraged a competitive atmosphere in training.
But the last thing he needed was an issue with Martial, as the Frenchman is expected to play a key role after the World Cup following Ronaldo's TV meltdown.
The Portuguese's explosive interview with Piers Morgan on Talk TV means there is no way back.
Martial, who has struggled with injuries again this season, is back to full fitness and Ten Hag believes he can give United a cutting edge in attack.
